Many different cast concrete moldings are known. Such pre-cast bricks are used to build free-standing or retaining walls. The present invention concerns a new pre-cast brick of this type and a process and apparatus for the industrial manufacture of the brick. The conventional manner of manufacturing such concrete elements is to cast them in varied shapes by means of a special apparatus. This is principally done using a box-shaped mold with the negative shape of the finished element on the inside. This mold is placed on a support board, the board being pushed onto a vibrating table by a special board carriage running on tracks. The table functions as a main vibrator and is located beneath the support board. The mold cavity is then filled with concrete. This is done by a mobile hopper which is loaded automatically from a storage tank containing ready-mixed concrete. Concrete passes from the storage tank into the mobile hopper through a spout. As soon as the mold is full of concrete, the mobile hopper is moved back into position beneath the storage tank spout, and a plunger descends upon the concrete in the mold. The cross-section of the plunger is identically matched to the top outside surface of the finished molding. Usually the plunger is hydraulically pressed down on the concrete in the mold. Simultaneously, it also works as a vibrator at the top of the mold, while a main vibrator located under the bottom of the mold. i.e., beneath the board carriage, works together with the vibrations from the plunger. Thus, vibration comes from both above and below at the same time as the plunger is being pushed down, resulting in substantial compression of the concrete in the mold. Every angle and corner of the mold is thus optimally filled with concrete. As a result of the compression, the concrete reaches a level of hardness that permits immediate de-molding of the finished element. To this end, the mold is raised vertically along the plunger and over it, while the plunger itself remains in position, pressing down the concrete. As soon as the lower edge of the mold has been raised above the plunger surface, the plunger is carried along by the mold and raised with it. The finished pre-cast brick now remains in its de-molded form on the support board and is pushed away by the board carriage for onward transportation by a conveyor system. The empty board carriage is then moved back into position. On its return journey, it pushes another support board onto the main vibrator. Now, the box mold is lowered back onto the support board and re-filled with concrete. In this conventional process, the pre-cast element is always vertically de-molded by raising the mold perpendicularly. It is the inside surfaces of the mold that determine what kind of external side and visible upper surfaces the finished element will have, with the exception of the top. Due to the vertical movement of the mold during de-molding, it is not possible to shape any surfaces of the finished casting other than those listed above.
To build retaining walls at varying angles of incline, special retaining wall elements in the shape of an open trough, for example, may be used. The individual elements are built into the slope which is to be retained starting from the bottom and working up. The layers of these elements usually recede somewhat, which means that each succeeding level is slightly further back than the one beneath it by a distance determined by the steepness of the slope. The elements themselves have stops which effectively prevent one element from being pushed out in front of the one below it. At the same time, these stops determine the maximum angle of incline that can be retained with elements of that particular kind. It would be especially desirable for the purpose of building up retaining systems for slopes to have elements with an overhanging front, because this would make it possible to retain much steeper slopes.
Conventional pre-cast elements have smooth sides due to the manner of the fabrication process, because the mold scrapes along these sides during de-molding. If these smooth sides remain visible in a retaining wall, their appearance is bare, artificial and unattractive.
It is desirable, therefore, to make pre-cast elements with variously textured visible surfaces, which would give a general appearance of natural stone. Until now, it has not been possible to manufacture a pre-cast concrete brick with, for instance, an overhanging and textured visible front, due to the fact that the mold is removed vertically upwards.